Testing the Intake Air Temperature Sensor

What Is a Bad Intake Air Temperature (IAT) Sensor?

A bad intake air temperature (IAT) sensor may cause one or more of the following symptoms:

• stumbling during acceleration,
• difficulty starting,
• rich or lean air-fuel ratio,
• lean misfire (usually in a cold engine),
• rough idling when engine is cold,
• surging when engine is warm,
• increased fuel consumption,
• engine stalling or surging,
• faulty EGR system (in some applications), or
• "check engine" light with diagnostic trouble codes P0112 or P0113.

The engine computer module (ECM) may be able to deal with a faulty IAT sensor without much of a problem. However, some engines rely on the IAT sensor to turn on the cold-start injector or operate the EGR valve. So, a faulty IAT sensor can make it difficult for an engine to start when cold.

The ECM uses the IAT signal, along with information about air volume, to calculate the amount of oxygen entering the engine. It uses this information to fine-tune control of:

• fuel metering,
• air flow,
• ignition timing, and
• EGR valve opening (on some models).

1. Can a Faulty IAT Sensor Turn on the Check Engine Light?

In most cases, a problem with the IAT sensor will trigger a trouble code. Scanning your car's computer, you may find one or both of the following trouble codes:

• P0112: Intake air temperature sensor circuit low (voltage) input
• P0113: Intake air temperature sensor circuit high (voltage) input

Basically, your IAT sensor may fail in one or more of these ways:

• Failed IAT sensing element
• Contamination of the IAT sensor tip
• Loose or bad circuit connections
• Faulty circuit wiring
• Corroded or contaminated connector

Whether you find a sensor-related DTC or not, if you suspect a problem with the IAT sensor, you should:

• Check the sensor itself.
• if necessary, inspect the wiring and connectors in the sensor's circuit.
• Check for a dirty or clogged air filter.

The next step would be to follow the procedure here to help you test your IAT sensor and confirm failure before replacing it.

Before you start, though, it is a good idea to have the vehicle repair manual for your particular vehicle model when diagnosing potential problems. Your manual will have configuration information and electrical value specifications you may need during your diagnostic.

If you don't have this manual yet, you can buy a relatively inexpensive aftermarket manual from Amazon. Haynes manuals come with step-by-step procedures, wiring diagrams and illustrations for many maintenance, diagnostic and component replacement procedures you can do at home. You'll recoup your small investment quickly.

2. Intake Air Temperature Sensor Location

Depending on your particular vehicle model, you can find the IAT sensor in the following locations:

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• Intake air duct
• Intake air passage, on models with a manifold absolute pressure (MAP) sensor
• Intake plenum
• On some module with a mass air flow (MAF) sensor, the IAT is incorporated into the same housing
• On some models with a manifold absolute pressure (MAP) sensor, the IAT is built into the sensor as well.

If necessary, consult your vehicle repair manual to locate the sensor.

3. Different Names for the IAT Sensor

Depending on your particular model (especially older models), you may find your sensor listed under one of the following names:

• manifold air temperature (MAT) sensor
• charge temperature sensor (CTS)
• air charge temperature (ACT) sensor
• inlet air temperature sensor
• vane air temperature (VAT) sensor
• air temperature sensor (ATS)
• manifold charging temperature (MCT) sensor

4. Testing the IAT Sensor

The IAT sensor is a thermistor that changes electrical resistance with changes in temperature. You can take advantage of the way the IAT sensor works to test sensor operation using an ohmmeter. But first, locate the IAT sensor in your particular vehicle.

If the IAT sensor in your vehicle is part of the MAF or MAP sensor, you may need to test the sensor in the vehicle while checking its resistance or voltage. Also, consult your vehicle repair manual to identify the IAT sensor wires.

Keep in mind that your sensor will increase (PTC) or decrease (NTC) resistance as temperature increases, depending on the type of sensor your vehicle uses. If necessary, consult your vehicle repair manual to verify your particular application. The following tests assume you have an NTC type sensor.

You can use the next two tests, if your IAT sensors is an integral part of the MAF or MAP sensor; but they can also work for independently mounted sensors as well.

Make sure your engine is cool before you start the next test.

a) Checking IAT Sensor Resistance

1. Unplug the IAT sensor electrical connector.
2. Set your digital multimeter to over 50K on the Ohms scale or to auto range.

3. With the engine off, measure the sensor resistance across its terminals.

   • At about 68 F (20 C), you should get around 37K ohms
   • At about 86 F (30 C), you should get around 24K ohms
4. Plug in the sensor electrical connector.
5. Start the engine and let it idle for about 20 minutes or until the cooling fan comes on to allow the engine to reach operating temperature.
6. Turn off the engine.
7. Unplug the IAT sensor electrical connector.

8. With the engine off, measure again the sensor resistance across its terminals.

   • At about 194 F (90 C), you should get around 2.8K ohms
   • At about 212 F (100 C), you should get around 2K ohms

You can use the following table as a general reference of temperature-resistance values. However, consult your vehicle repair manual for the specifications for your particular model.

Temperature and Resistance Values of an IAT Sensor

b) Checking the IAT Sensor Power and Ground Circuit

This test will check that your car's computer is providing the IAT sensor with 5 volts (reference voltage) and ground to complete the circuit.

1. Turn off the engine. Wait for the engine to cool, if necessary.
2. Set your DMM to the DC voltage scale.
3. Unplug the IAT's electrical connector.
4. Using the DMM's red lead, back probe the IAT's signal wire on the connector. Consult your repair manual to identify this wire, if necessary.
5. Connect your DMM's black lead to engine ground or the battery negative (-) post.

6. Turn the ignition key to the On (Run) position, but don't start the engine.

   • Your meter should register 4.5 to 5 volts. If not, check that part of the circuit. Head over to the section Checking the IAT Wires.
7. Turn the ignition key off.
8. Now, with the IAT's electrical connector still unplugged, back probe the IAT's ground wire with the black lead of your DMM.
9. Connect your DMM's read lead to battery voltage.

10. Turn the ignition key to the On (Run) position, but don't start the engine.

    • Your meter should register 12V approximately. If not, check that part of the circuit. Head over to the sections Checking the IAT Wires.
11. Turn the ignition key Off.
12. Plug back in the IAT's electrical connector.

Consult your vehicle repair manual to identify the wires and check specifications, if necessary.

5. Testing the IAT Sensor Off the Vehicle

If you can remove the sensor off the engine, you can also test the IAT sensor using water, a thermometer and your Ohmmeter.

1. Remove the IAT sensor from the engine. Consult your vehicle repair manual, if necessary.
2. Examine the sensor's tip, electrical connector and terminal for contamination or damage.
3. Clean the sensor's tip and terminal with electronic cleaner, if necessary.
4. Fill a container with water and place the IAT sensor in it.
5. Use a kitchen thermometer or infrared thermometer, if possible, to measure water temperature.
6. Connect your Ohmmeter across the IAT sensor terminals.
7. Place the container on a stove and heat the water.
8. Watch the resistance reading as the water heats up and record the resistance and temperature at different intervals.
9. Compare your readings to your repair manual specifications.

You Can Test the Sensor Using a Blow Drier:

1. Unplug the sensor electrical connector.
2. Remove the sensor from the vehicle.
3. Examine the sensor's tip and electrical connector and terminal for contamination or damage.
4. Connect your ohmmeter leads to the sensor electrical terminals.
5. Clean the sensor's tip and terminal with electronics cleaner, if necessary.
6. Check the sensor resistance.
7. Begin warming up the sensor tip with the blow drier.
8. Watch the sensor resistance as the tip of the sensor warms up.
9. Compare the sensor resistance changes to specifications.

The sensor resistance should gradually and smoothly begin to decrease as you begin to warm up the tip. If necessary, compare your readings to specifications.

If you found no change in the sensor resistance or changes were erratic, replace the IAT sensor.

When installing a new sensor or reinstalling the original sensor, you may need to use teflon tape or sealant on the sensor threads to prevent air leaks. Consult your vehicle repair manual, if necessary.

6. Checking the IAT Sensor Wires

This test can help you locate a possible bad wire in the circuit.

1. Check the connectors at the sensor and computer side for a loose wire or contamination that might be preventing a good connection.
2. Check the wiring harness for a damaged wire that might be preventing electrical flow.

3. Measure the wires' resistance.

   • With the wiring harness disconnected from the sensor and computer, measure each wire resistance with your ohmmeter.
   • The wire should show approximately 0 ohms of resistance.
   • If one of the wires show infinite resistance, that wire is broken.

If you still find no problems, the fault may be with the computer driver. Bring in your vehicle to a repair shop for a diagnostic.

7. Replacing the IAT Sensor

For the most part, replacing a faulty IAT sensor is a straightforward procedure.

If the Sensor Is Mounted by Itself on the Intake Air Duct:

1. Turn off the engine.
2. Disconnect the negative battery cable.
3. Unplug the IAT sensor electrical connector.
4. Carefully pull the sensor off the duct.
5. Mount the new sensor and plug in the electrical connector.
6. Connect the negative battery cable.

If the Sensor Is Mounted on the Intake Manifold:

1. Turn off the engine.
2. Disconnect the negative battery cable.
3. Unplug the IAT sensor electrical connector.
4. Unscrew the sensor using a wrench.
5. Install the new sensor and plug in the electrical connector.
6. Connect the negative battery cable.

If the sensor is an integral part of the MAF or MAP sensor, replace the MAF or MAP sensor.

8. Testing Your IAT Sensor to Save Time and Money

In most cases, problems with the IAT sensor come form the sensor itself. Sometimes, you'll be dealing with a faulty harness or connector. Even more rare is a computer driver fault.

And testing for a bad IAT sensor is a simple procedure most car owners can do themselves. A bad IAT sensor will have a more significant effect on engine performance during the extreme months of winter and summer, and a considerable effect on emission levels.

So whenever you suspect a bad IAT sensor or your car's computer stores a code or codes pointing to a bad IAT sensor or circuit, use these tests before you replace the sensor. Problems with other sensors or systems may cause similar symptoms produced by a faulty IAT sensor. So this diagnostic procedure will save you time and money.

The following video gives you a quick overview of testing an IAT sensor using a multimeter.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Dan Ferrell